There is no one best set of tactics in the "Soccer Manager" fantasy sports game. The success of any set of tactics is based on how well it fits the personnel used on the pitch.
The first thing to consider when selecting tactics is the formation the team will play. Formation should be selected based on the types of players at the player's disposal and the weaknesses of the player's opponents. Players should be used in their preferred positions whenever possible.
Bench players should be picked based on the balance of the starting squad. For example, a team with three starting forwards should have at least one extra forward on the bench, which will benefit the team in the event that a starting forward gets tired or injured.
Team instructions should be chosen based on the strength of the selected players. For example, if a team's players are defensively strong, instructions that emphasize those qualities will work better than instructions that emphasize attacking skill. Individual player instructions (who will be captain, penalty taker, corner taker, etc.) should be based on individual strengths.
In-game instructions will change a team's formation and playing style based on the time and situation of any given match. As a general guideline, defensive instructions (more defenders and players behind the ball) should be used when the team is in the lead late in the match, and attacking instructions (more forwards and players pushing up the pitch) should be used when the team is trailing late in the match.